The inventive concepts described herein generally relate to memory devices, and more particularly, the inventive concepts relate to variable resistance memory devices and to methods of programming variable resistance memory devices.
Non-volatile memory devices are widely used in many consumer, commercial and other applications. While some non-volatile memory devices, such as flash memory, use accumulated charge to store data, some other memory devices, such as resistive random access memory (ReRAM), phase change RAM (PRAM), and magnetic RAM (MRAM), use changes in resistivity of a material therein as the mechanism by which data is stored.
A resistive random access memory (ReRAM) is a non-volatile memory device that uses changing resistance characteristics of a material having a variable resistance that changes significantly at a particular voltage. In one example, the material may be a transition metal oxide (TMO). When a “SET” voltage is applied to a variable resistance material, a resistance of the variable resistance material decreases. This state is typically referred to as a SET state or an ON state. When a “RESET” voltage is applied to a variable resistance material, the resistance of the variable resistance material increases. This state is typically referred to as a RESET state or an OFF state.
FIGS. 1A and 1B illustrate exemplary ReRAM memory cells. In the example of FIG. 1A, the ReRAM memory cell includes a diode DP and variable resistance element RP connected in series between a bit line BL and a word line WL. In the example of FIG. 1B, the ReRAM memory cell includes a transistor N1 and a variable resistive element RP connected in series between a bit line BL and a reference potential (VSS), with a gate of the transistor N1 connected to a word line WL. In these examples, the diode DP and transistor N1 function as switching elements responsive to voltages applied to the bit line BL and/or word line BL.